The present invention relates to fillers useful for aesthetic dental materials. In particular, the filler is a combination of nano-sized particles and clusters of nano-sized particles, where the former, due to their size and shape, reside in the interstitial spaces between the clusters.
Dental materials have special requirements. For health reasons, dental materials should be suitable for use in the oral environment. In certain applications, strength and durability of a dental material is important to ensure satisfactory performance. For example, for dental work at locations where mastication forces are generally great, high strength and durability is desirable. In other applications, an aesthetic character (e.g., luster and translucency) is desired. This is often the case where dental work is performed at locations where a tooth repair or restoration can be seen from a relatively short distance.
Strength in a dental material is typically achieved by adding fillers. Generally, a dental material has greater mechanical strength when it contains fillers having an average diameter greater than 0.4 to 0.6 micrometers. A disadvantage to these dental materials, however, is their tendency to lack luster and aesthetic character. Another disadvantage of composites with such average particle size is that with repeated toothbrushing (a requirement for oral hygiene), the hardened resin can wear away leaving a dull, unaesthetic surface. The worn surface can be a site for subsequent plaque accumulation.
Some skilled in the art have investigated using a combination of different average particle size fillers to improve the aesthetic character of the dental material.
For example, U.S. Pat. No. 5,936,006 (Rheinberger et al.) discloses a filled and polymerizable dental material characterized in that it contains a sol of amphorous SiO2 particles in a liquid, organic dispersion agent, the SiO2 particles being organically surface modified, having an average size of 10 to 100 nm and being non-agglomerated. The sol is referred to as xe2x80x9csilica organosol (a).xe2x80x9d The SiO2 particles of the silica organosol (a) are organically modified at the surface. The dental material can also contain at least one polymerizable organic binder (b), and can contain conventional inorganic or organic particle-shaped fillers (c).
WO 00/03688 provides a dental enamel material having an opacity less than 50 percent and localized wear volume loss less than 0.025 mm3. The material comprises a polymerizable matrix forming liquid having a first refractive index (ND) and inorganic filler particles having a second ND. The first ND is within 5 percent of the second ND. The filler comprises particles of (a) low median particle size between 0.1 and 1.0 micrometers and (b) high median particle size between 1 and 10 micrometers. Preferred filler material is radiopaque dental glass such as barium aluminum-borosilicate glass, barium aluminofluorosilicate glass, and mixtures thereof. It is stated that the dental enamel material exhibits similar or improved physical characteristic when compared to known dental composites. Such physical characteristics include, among other things, opacity improvements, diametral tensile strength, polymerization shrinkage, and wear.
WO 99/65453 provides a dental composite comprising a resin base and a structural filler of ground particles having an average particle size between 0.05 and 0.5 micrometer. It is explained that because the structural filler particles are ground, they are non-spherical, providing increased adhesion of the resin to the structural filler. This increased adhesion is said to enhance the overall strength of the composite. The dental composite is said to provide the luster and translucency required for cosmetic applications. The structural filler is ground, typically by agitator milling, to the preferred mean particle size. This grinding-method is distinguished from the sol-gel process, in that the grinding method results in non-spherical particles.
Although the foregoing technology may provide useful dental materials, other compositions are sought.
The present invention provides a dental material having a unique combination of filler particles: nano-sized particles and clusters of nano-sized particles (often referred to as xe2x80x9cclustersxe2x80x9d for convenience). It has been discovered that this combination provides a syngeristic effect that results in enhanced performance, as shown by the properties, of the inventive material. It is currently believed, as shown by transmission electron microscopy, that the smaller nano-sized particles fill the interstitial spaces between the larger clusters thereby minimizing voids in the composite dental material.
In brief summary, the inventive material comprises (a) a hardenable resin; and (b) a filler comprising (i) clusters of nano-sized particles, the clusters comprising non-heavy metal oxide particles and heavy metal oxides, and being not fully densified particles and (ii) non-agglomerated nano-sized particles selected from the group consisting of non-beavy metal oxide particles, heavy metal oxide particles, and combinations thereof. Preferably, the inventive material comprises a filler comprising at least about 60% by weight of the clusters and at most about 40% by weight of the nano-sized particles, based on the total filler. The material is a dental material.
In brief summary, the inventive material comprises (a) a hardenable resin; and (b) fillers comprising (i) clusters of nano-sized particles, the clusters comprising non-heavy metal oxide particles and heavy metal oxides, and being not fully densified particles; (ii) non-agglomerated nano-sized particles selected from the group consisting of non-heavy metal oxide particles, heavy metal oxide particles, and combinations thereof. The material is a dental material.
A method of making the inventive dental material comprises the acts of: (a) providing a hardenable resin; (b) providing a powder of filler particles comprising (i)-clusters of nano-sized particles, the clusters comprising non-heavy metal oxide particles and heavy metal oxides, and being not fully densified and (ii) non-agglomerated nano-sized particles selected from the group consisting of non-heavy metal oxide particles, heavy metal oxide particles, and combinations thereof, (c) surface treating the filler particles to yield surface-treated filler particles; and (d) mixing the surface treated filler particles with the hardenable resin.
A method of making the inventive dental material comprises the acts of: (a) providing a hardenable resin; (b) providing a powder of filler particles comprising (i) clusters of nano-sized particles, the clusters comprising non-heavy metal oxide particles and heavy metal oxides, and being not fully densified; (ii) non-agglomerated nano-sized particles selected from the group consisting of non-heavy metal oxide particles, heavy metal oxide particles, and combinations thereof, (c) surface treating the filler particles to yield surface-treated filler particles; and (d) mixing the surface treated filler particles with the hardenable resin.
The clusters provide, among other things, strength while the nano-sized particles provide, among other properties, aesthetic quality, polishability, and wear resistance to the inventive material. Although the clusters and the nano-sized particles are structurally different types of fillers, they can have similar chemical constituents. Depending on the composition of the clusters and resin, one can add nano-sized non-heavy metal oxide particles, and/or heavy metal oxide particles to optimize the visual opacity and other properties of the inventive material. In this way, the present invention allows for flexibility in matching the refractive index of the components to minimize visual opacity. As a result, the inventive material exhibits excellent aesthetic quality while providing desirable properties. Such properties include, but are not limited to, good tensile strength, compressive strength, polishability, wear or abrasion resistance, luster, and low shrinkage after cure. Although low visual opacity is typically a desired property, it is not necessary for posterior applications.
The inventive material can be used in dental applications. Such applications include dental adhesives, artificial crowns, anterior or posterior fillings, casting materials, cavity liners, cements, coating compositions, mill blanks, orthodontic devices and adhesives, restoratives, prostheses, and sealants. The materials can be placed in the mouth and cured or hardened in situ. Alternatively, it may be fabricated into a prosthesis outside the mouth and subsequently adhered in place in the mouth.
As used herein,
xe2x80x9cAesthetic qualityxe2x80x9d of a material, particularly a dental material, tends to be a subjective characteristic and yet a well-understood property in the dental industry. It can be quantified by visual opacity and/or polishability.
xe2x80x9cHardenablexe2x80x9d is descriptive of a material that can be cured or solidified e.g., by heating to remove solvent, heating to cause polymerization, chemical crosslinking, radiation-induced polymerization or crosslinking, or the like;
xe2x80x9cNon-heavy metal oxidexe2x80x9d means any oxide of elements other than those of heavy metals.
xe2x80x9cPolishabilityxe2x80x9d is a property that can influence a material""s aesthetic quality. Polishability is a measure of the retained gloss, i.e., polish retention and luster of a material after repeated abrasive contact, such as after tooth brushing.
xe2x80x9cVisual opacityxe2x80x9d is a property that can influence a material""s aesthetic quality. In general, a low the visual opacity value is desirable.